Gas turbine engines include fuel nozzles to deliver combustion fuel to combustor components. Over a period of extended use, fuel nozzles may experience deterioration, e.g, around the edges of the nozzle tip. There is currently no efficient process available to repair a primary fuel nozzle that is manufactured with a brazed joint between the nozzle tip and the body of the nozzle. Any process to build a metal layer by traditional fusion welding poses a risk that the brazed joint may be damaged by the heat applied by the welding process. Also, distortion induced by the welding process may not be acceptable for the tolerances required of turbine components such as a primary fuel nozzle. In order to avoid the risks associated with fusion welding, a process with a low heat input has to be used. Laser cladding may be sufficiently low temperature for restoring a nozzle tip to the correct dimensions, but depositing metal on the edge of a nozzle using laser cladding techniques is difficult.
An electrospark deposition (ESD) process is known to have a very low heat input. The ESD transfers stored energy to a consumable electrode, e.g., carbides (W, Ti, Cr etc) stainless steel, aluminum, and other electrode compositions. The temperature on the tip of the electrode may be in a range of about 5000 to about 10,000° C. The electrode material is ionized and transferred to the substrate surface, producing an alloy with the substrate and a deposition on the alloyed electrode-substrate interface. The deposited layer bonds metallurgically on the alloyed substrate and electrode material.
ESD is used for cosmetic repair of gas turbine components. One challenge that the ESD process must overcome is overheating of the electrode and the local substrate, e.g., in a fuel nozzle, where a brazed joint may be compromised by local heating caused by welding or ESD techniques. What is needed is a local cooling process that provides ESD on a fuel nozzle without overheating the electrode and local substrate.
Intended advantages of the disclosed systems and/or methods satisfy one or more of these needs or provide other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.